This project seeks to understand the molecular interactions whereby proteins control the activity of imbedded metal ions, which are known to carry out key biochemical reactions, including electron transfer an oxygen activation. Systems of interest include the iron-sulfur class of proteins, copper proteins, molybdenum proteins, and vanadium proteins. Resonance Raman spectroscopy is used to probe structural details of the active sites in important functional states. Further development of the method to increase its utility is an essential part of the program.